[unreadable] Transient structural changes during neural activity are directly related to the action potential propagation. The first non-contact optical measurement of these fast (approximately 1 millisecond) and small (approximately 1 nanometer) changes (Akkin, 2003; Akkin et al., 2004) has been recently reported by using differential phase contrast optical coherence tomography (DPC-OCT) [1,2]. The measurements are depth-resolved and do not require exogenous chemicals or reflection coatings. The method, highlighted as of special interest in a review article [3], is innovative and is expected to have a major impact in neuroscience. The long term objective is to elucidate the origin of the transient structural changes and its contributions to the optical indications of neural activity. The hypothesis behind the work is that the transient structural changes in the active nerve, despite its small magnitude, is a major contributor to many optical signals indicating the neural activity. The hypothesis is derived from the following observations: (i) 1 nm swelling is approximately 1,800 times greater than the retardation change (AR) reported for a squid giant axon. The retardation is the product of birefringence (an optical property) and thickness, (ii) The non-contact measurements revealed nanometer scale swelling and shrinkage. Similarly, positive and negative changes in retardation and light scattering have been reported for different preparations that are both potentially related to the transient thickness change. Based on these observations, the specific aims of our proposed research are designed to correlate the transient structural changes and the optical signals indicating the neural activity. [unreadable] [unreadable] [unreadable]